Composition and method to form displacements for use in metal casting

ABSTRACT

A method to form a displacement, the method including disposing a powder blend comprising a plurality of ground ceramic particles and a plurality of ground resin particles into a mold, densifying the powder blend while in the mold, heating the mold to form a first displacement, impregnating said first displacement with a polymer precursor compound to form a second displacement, and heating the second displacement to form a third displacement.

INCORPORATION BY REFERENCE

U.S. Pat. No. 8,506,861 is incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to a composition and method to form one or more displacements for use in a metal, ceramic, or cermet casting process. In certain embodiments, the invention is directed to a composition, and method using that composition, to form one or more displacements for use in a metal, ceramic, or cermet casting process.

BACKGROUND OF THE INVENTION

Foundry work involves the introduction of molten metal into a mold, which is formed to contain a hollow cavity defining a desired shape. Sand casting is one of the most popular and simplest types of casting because it allows for flexible sizes of batches and provides reasonable cost.

The first step in the sand casting process is to create the mold. The sand is packed around the pattern to replicate the external shape of the casting. The cavity that forms the casting remains when the pattern is removed. Lubrication is often applied to the surfaces of the mold cavity in order to facilitate removal of the casting.

In certain embodiments, internal features of the casting are defined by separate displacements which are prepared prior to molding process.

SUMMARY OF THE INVENTION

Applicants' disclosure provides a method to form a displacement for use in the metal casting process, wherein the method provides a plurality of ceramic particles and a plurality of resin particles. The method further grinds the plurality of ceramic particles until those ceramic particles comprise a maximum dimension less than about 150 microns. The method further grinds the plurality of resin particles until those resin particles comprise a maximum dimension less than about 100 microns. The method subsequently forms a powder blend consisting of a mixture of the plurality of ground ceramic particles and the plurality of ground resin particles. In certain embodiments, the powder blend comprises a plurality of ground ceramic particles, a plurality of ground resin particles, and a plurality of reinforcing fibers. In other embodiments, the powder blend comprises a plurality of ground ceramic particles, a plurality of ground resin particles, and a cylindrical graphite member.

Applicants' disclosure also provides further treatments of the displacement for use in the metal casting process. These additional treatments enhance the mechanical strength so that the displacement will better survive the molten metal molding process.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from a reading of the following detailed description taken in conjunction with the drawings in which like reference designators are used to designate like elements, and in which:

FIG. 1 illustrates a cross-sectional view of a metal casting mold;

FIG. 2A shows a perspective view of a metal casting with displacement 110A/110B still inserted therein;

FIG. 2B shows a perspective view of metal molding 202, wherein displacement 110A/110B have been removed;

FIG. 3 is a flow chart summarizing the steps of Applicants' method to form a casting displacement without glassy carbon moieties; and

FIG. 4 shows a flow chart summarizing the steps of Applicants' method to form a casting displacement comprising glassy carbon moieties.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention is described in preferred embodiments in the following description with reference to the Figures, in which like numbers represent the same or similar elements. Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

The described features, structures, or characteristics of the invention may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are recited to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention may be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

Referring now to FIG. 1, casting metal mold 100 comprises displacement 110, cavity 120, chaplets 130 and 140. Displacement 110 is positioned within cavity 120 and fastened by chaplets 130 and 140. Liquid molten metal is then introduced into mold 100. Liquid molten metal is introduced into mold 100 to fill entire cavity 120. The molten metal that is poured into the mold then begins to cool and solidify.

When the entire cavity 120 is filled and the molten metal solidifies, the final shape of the casting is formed, wherein any internal holes and passages of the casting are formed due to the insertion of displacement 110.

FIG. 2A illustrates metal molding 200, wherein a distal end 110B of displacement 110 (FIG. 1) extends outwardly from end 205 of molding 200. FIG. 2B illustrates metal molding 202, wherein displacement portions 110A and 110B have been removed. In certain embodiments, displacement portions 110A and 110B are removed using a water spray under pressure.

Applicants' disclosure comprises a method to form displacement 200. In certain embodiments, the displacement can be a complex displacement. For example, as illustrated in FIG. 2B, the complex displacement comprises a cylindrical body 204 formed to include an aperture 210 extending inwardly from distal end 205, wherein cylindrical body comprises a first diameter, in combination with an integral annular lip 215 disposed around proximal end 207 of cylindrical body 204, wherein annular ring 215 comprises a second diameter, wherein the second diameter is greater than the first diameter.

FIG. 3 summarizes the steps of Applicants' method to form displacements for metal casting process using Applicants' molding composition. Referring now to FIG. 3, in step 310 Applicants' method provides a ceramic powder. In certain embodiments, that ceramic powder is selected from the group consisting of, but not limited to, silica, zirconia, olivine, magnesium oxide, silica carbide, aluminum oxide, and combinations thereof. In certain embodiments, the ceramic powder is a mixture of silica and aluminum oxide. Applicants have found that if a molding composition comprises mostly silica, the molding composition does not have a sufficient compression strength and cracks when the molding composition is fired at 1000° C.

Step 320 further comprises providing a resin system. In certain embodiments, the resin system of step 320 comprises a thermosetting adhesive composition. In certain embodiments, the thermosetting resin system of step 310 is selected from the group consisting of a phenol-formaldehyde resin, a resorcinol-formaldehyde resin, a resol resin, a novalac resin, and a melamine resin. As those skilled in the art will appreciate, melamine resins are formed by a reaction of dicyandiamide with formaldehyde.

As those skilled in the art will appreciate, phenolic resins, melamine resol resins, novalacs, and formaldehyde resins comprise strong bonds and exhibit good resistance to high temperatures. In certain embodiments, Applicants' resin system comprises a one part system that cures with heat or heat and pressure. In other embodiments, Applicants' resin system comprises a resin, as described above, in combination with a hardener, wherein the resin system crosslinks, i.e. cures, with the application of heat.

In certain embodiments, Applicants' hardener comprises a diamine. In certain embodiments, Applicants' hardener comprises an aromatic diamine, such as and without limitation to luene diamine, diphenylmethane diamine, and the like. In certain embodiments, Applicants' hardener comprises an alkyl diamine, such as and without limitation, hexamethylene diamine.

In step 330, Applicants' method grinds the ceramic powder of step 310. Applicants have found that the ceramic powder must be ground to smaller than 100 microns. Applicants have found that use of powders having particles with diameters larger than about 150 microns result in the formation of displacements that comprise insufficient mechanical properties during the high temperature metal casting process.

In certain embodiments, step 330 comprises grinding the ceramic powder of step 310 until the particles comprising that powder comprise diameters less than about 150 microns. By “about,” Applicant means plus or minus ten percent (10%). In certain embodiments, step 330 comprises forming a ceramic powder comprising particles having maximum dimensions less than about 150 microns and greater than about 30 microns. In certain embodiments, the average particle maximum dimension is about 75 microns.

In step 340, Applicants' method grinds the resin system of step 320. Applicants have found that the resin system must be ground to smaller than 150 microns. Applicants have found that use of resin systems comprising particles with a maximum dimension larger than about 150 microns result in the formation of displacements that comprise insufficient mechanical properties during the high temperature metal casting process.

In certain embodiments, step 340 comprises grinding the resin system of step 310 until the particles comprising that powder comprise maximum dimensions less than about 150 microns. In certain embodiments, step 340 comprises providing a resin system comprising particles having maximum dimensions less than about 150 microns and greater than about 30 microns. In certain embodiments, the average particle maximum dimension is about 75 microns.

In step 350, Applicants' method determines if a fiber reinforcement will be used. In certain embodiments, Applicants' displacements for metal casting process are formed without a fiber reinforcement. On the other hand in certain embodiments, Applicants' displacements are formed using one or more fiber reinforcements. If Applicants' method elects not to use a fiber reinforcement, then the method transitions from step 350 to step 370.

If Applicants' method elects to use a fiber reinforcement, then the method transitions from step 350 to step 360 wherein the method provides a plurality of reinforcing fibers. In certain embodiments, Applicants' reinforcement fiber comprises carbon fiber. In certain embodiments, Applicants' reinforcement fiber comprises fiber glass. Applicants have found that fiber glass reinforcement fibers comprise a low coefficient of thermal expansion in combination with a high thermal conductivity. As a result, fiber glass reinforced displacements comprise a dimensionally stable material that more rapidly dissipates heat as compared to asbestos and organic fibers.

In certain embodiments, Applicants' fiber glass comprises a fiber glass mat. In certain embodiments, Applicants' fiber glass comprises a plurality of uncoated milled fibers comprising about a 200 micron length.

Applicants have found that using reinforcing fibers comprising a nominal length of about 200 microns imparts the optimal combination of mechanical strength and surface smoothness to the cured displacements. More specifically, Applicants have found that using displacements comprising reinforcing fibers comprising a nominal length of about 200 microns results in optimal cavity formation in the metal casting process. Applicants have further found that use of longer fibers results in only a minimal mechanical property enhancement but also further results in a much rougher surface.

Applicants' method transitions from step 360 to step 370 wherein the method blends the ceramic powder, resin system, along with the optional fiber reinforcement of step 360. In certain embodiments, step 370 comprises using a twin shell V blender for approximately 30 minutes using ⅛″ alumina media to insure a nearly homogenous mixture.

Applicants' method transitions from step 370 to step 375 wherein the method loads this blended composition of step 370 into the mold provided in step 310. In step 380, Applicants' method densifies the blended composition disposed in the mold.

In certain embodiments, step 380 includes using isostatic pressing to densify the blended ceramic, resin, and reinforcement. In certain embodiments, step 380 includes using uniaxial pressing to densify the blended ceramic, resin, and reinforcement. In certain embodiments, step 380 includes using vibration to densify the blended ceramic, resin, and reinforcement.

In certain embodiments, the blended composition of step 370 comprises between about 50 to about 95 weight percent ceramic powder, between about 5 to about 25 weight percent resin system, and between about 0 to about 25 weight percent reinforcing fiber. As described herein, “about” is used to mean that a difference in weight percentage is plus or minus ten percent (10%). As a general matter, the weight percentage of resin system increases as the average particle dimension of the ceramic powder decreases. The weight percentages of the ceramic powder, the resin system, and the reinforcing fiber are adjusted respectively to achieve a certain Grain Fineness Number (AFS 11-6-00-S) to ensure a particular particle size distribution in the molding composition.

As those skilled in the art will appreciate, a Grain Fineness Number (“GFN”) is a concept developed by the American Foundry Society for rapidly expressing the average grain size of a given particle distribution. It approximates the number of microns per inch of that sieve that would just pass the sample if its grains of uniform size. It is approximately proportional to the surface area per unit of weight of sand, exclusive of clay.

The optimal grain fineness number (GFN) in a system is determined by the type of metal poured, pouring temperatures, casting product mix (heavy vs. light castings) and required surface finish. After that optimal fineness level is determined, maintaining a consistent grain structure becomes a critical factor in the quality of the final castings.

GFN is a measure of the average size of the particles (or grains).

Example I

The grain fineness of molding sand is measured using a test called sieve analysis, which is performed as follows:

1. A representative sample of the sand is dried and weighed, then passed through a series of progressively finer sieves (screens) while they are agitated and tapped for a 15-minute test cycle.

2. The particles retained on each sieve (grains that are too large to pass through) are then weighed and recorded.

3. The weight retained on each sieve is divided by the total sample weight to arrive at the percent retained on each screen.

4. The percentage of particles retained is then multiplied by a factor, or multiplier, for each particular screen (Table 1). The factors reflect the fact that the sand retained on a particular sieve (e.g. 50 microns) is not all 50 microns in size, but rather smaller than 40 microns (i.e. it passed through a 40 micron screen) and larger than 50 microns (it won't pass through 50 micron screen). The result should be rounded to one decimal place.

5. The individual screen values then are added together to get the AFS-GFN of the sand, representing an average grain fineness (Table 1).

This number is the weighted mathematical average of the particle size for that sand sample. Many metal casting facilities have developed computer spread sheets to perform these calculations, limiting the potential for human error.

By itself, GFN does not identify a good molding material, or produce the qualities needed in a particular metal casting sand system. Because GFN represents an average fineness, particle blends comprising resin particles in combination with ceramic particles with very different grain size distribution may have similar GFN numbers. This being the case, the distribution of grains on the screens is another critical factor. The distribution refers to the quantity of particles retained on each individual sieve, rather than the average of all particles retained on all sieves.

Note: U.S screens are manufactured using inches as the measurement for the screen openings (openings per linear inch), as designated in ASTM E-11. Some screen manufacturers in Europe and Asia may have metric screen size openings. AFS measurements using metric screens will not compare directly to U.S.-based screen measurements.

TABLE 1 Mathematical Factors for Calculation of AFS-GFN (sample size of 78.4 g) Sieve Size on Sieve (g) Retained Multiplier Product* 6 Micron 0 0 0.03 0 12 Micron 0 0 0.05 0 20 Micron 0 0 0.1 0 30 Micron 0.7 0.9 0.2 0.18 40 Micron 3.9 4.9 0.3 1.47 50 Micron 19.4 24.7 0.4 9.88 70 Micron 37.3 47.6 0.5 23.8 100 Micron 16.3 20.8 0.7 14.56 140 Micron 0.8 1 1 1 200 Micron 0 0 1.40 270 Micron 0 0 2 0 TOTAL 78.4 100-50.89** *Product is percent retained times multiplier **AFS GFN = 50.9 (sum of all products rounded to one decimal) In step 385, Applicants' method initiates the cure of the displacement(s). In certain embodiments, step 385 comprises heating the mold at a temperature of about 200° C. for about one hour. As described herein, “about” is used to mean that a difference in temperature or length of time is plus or minus ten percent (10%). In certain embodiments, step 385 comprises using a forced air oven. In certain embodiments, step 385 comprises disposing the mold onto a conveyor belt that transports the mold through an oven. In certain embodiments, step 385 comprises using infrared heating.

In certain embodiments, the mold of step 310 is formed using a UV transparent material, and the binder of step 310 comprises a UV-curable binder, wherein in step 385 the mold is exposed to UV irradiation to effect the cure of the binder composition.

After the cure of the displacements at a temperature of about 200° C., the displacements can be machined into a final desired shape if a secondary machining is required in step 390. During step 395, the cured displacements from step 385 can be machined with high precision into casting products with different dimensions and requirements, such as threads. If a secondary machining is not required, the current method continues from step 390 to step 397.

Referring to step 397, in certain embodiments, the formed displacements from step 385 or step 395 are further treated to enhance their mechanical properties in preparation for the metal casting process. If the formed displacements from step 385 or step 395 need to have further property enhancement, the current method transitions from step 397 to step 440 (FIG. 4). To the contrary, if the formed displacements from step 385 or step 395 do not need further property enhancement, Applicants' method transitions from step 397 to step 399 and ends.

Because high combustibles and volatiles in the displacements cause pinholes, smoke, blows, gas, and rough surface in the casting product, the Applicants' method eliminates any material(s) or additive(s) in the displacements that will volatize when molten metal is poured onto the displacements. As a result, violent vaporization and/or thermal decomposition of any material in the displacements will not take place. Therefore, the metal casting comprises a smooth surface.

Moreover, displacements for metal casting need to have a sufficient compactability to avoid cuts and washes, friable broken edges, crushes, hard-to-lift pockets, penetration, and erosion scabbing. Also, the compactability cannot be too high to cause oversized castings.

Further, displacements need to have a balanced compressive strength to be strong under the pouring pressure of the liquid molten to avoid formation of inclusions, erosions, friable broken edges, etc.

Applicant has developed a supplemental method to enhance the mechanical properties of an as-formed displacement using the steps of FIG. 4. Referring now to FIG. 4, in step 410, the method provides (N) displacement articles for use in a metal casting system. In certain embodiments, one or more of the (N) displacements were previously formed.

In step 420, the method sets (i) equal to 1. In step 430, the method determines if an (i)th displacement article comprises satisfactory properties. If the method determines in step 430 that the mechanical and thermal properties of an original (i)th displacement are sufficient, then the method transitions from step 430 to step 432 wherein the method determines if (i) equals (N), i.e. if each of the (N) displacements of step 410 have been evaluated. If the method determines in step 432 that (i) equals (N), then the method transitions from step 432 to step 490 and ends. Alternatively, if the method determines in step 432 that (i) does not equal (N), then the method transitions from step 432 to step 434 wherein the method sets (i) equal to (i+1). The method transitions from step 434 to step 430 and continues as described herein.

If the method determines in step 430 that the mechanical and thermal properties of an original (i)th displacement are not sufficient, then the method transitions from step 430 to step 440, wherein a previously-prepared (i)th displacement is immersed in a mixture comprising one or more polymer precursor compounds, such as and without limitation, carbon-containing resins.

In step 450, the method heats at about 1000° C. an (i)th displacement impregnated with the one or more polymer precursors to form polymeric microstructures that are precursors to high-carbon solids, in combination with a conversion of these polymers to functional high-carbon solids, sometimes referred to as “glassy carbon.”

Glass-like carbon, often called glassy carbon or vitreous carbon, is a non-graphitizing, or nongraphitizable, carbon which combines glassy and ceramic properties with those of graphite. The most important properties are high temperature resistance, hardness (7 Mohs), low density, low electrical resistance, low friction, low thermal resistance, extreme resistance to chemical attack and impermeability to gases and liquids.

The structure of glassy carbon has long been a subject of debate. Early structural models assumed that both sp²- and sp³-bonded carbon atoms were present, but it is now known that glassy carbon is 100 percent sp² hybridized carbon. The structure of glassy carbon consists of long, randomly oriented microfibrils (15-50 A° wide) that bend, twist, and interlock to form robust interfibrillar nodes. More recent research has suggested that glassy carbon comprises a fullerene-type structure 1.

Glassy (or vitreous) carbon is typically a hard solid prepared by heat treatment at elevated temperatures of polymer precursors such as copolymer resins of phenolformaldehyde or furfuryl alcohol-phenol.

In certain embodiments, the polymer precursor compound(s) of step 440 is selected from the group consisting of furfuryl alcohol, phenol formaldehyde oligomer, acetone-furfural, furfuryl alcohol-phenol oligomer, polyvinyl chloride oligomer, polyvinylidene chloride oligomer, polyacrylonitrile oligomer, cellulose, and any combinations thereof.

In one embodiment, the displacement in step 440 is immersed in 10 percent by weight furfuryl alcohol 2 in chloroform, alcohol, benzene, ethanol, ethyl ether, water, acetone, or ethyl acetate, until a weight of the displacement stops increasing.

In certain embodiments, a catalyst is added to the furfuryl alcohol, such as a zinc chloride. In other embodiment, a catalyst is not added.

In step 450, the displacement, after soaking, is fired at about 1000° C. with a temperature ramp rate of about 60° F./hour for about 24 hours under an inert atmosphere to first form polymeric material 3 between the ceramic powder (provided in step 310) particles, wherein polymer 3 reinforces the previously formed displacement.

In certain embodiments, polyunsaturated sequences are formed by successive hydride/proton abstractions from certain methylene groups in polymer 3 to form polymer 4 comprising only sp² hybridized carbon atoms.

During the heating of step 450, polymer 3 and/or polymer 4 are continuously converted into the fullerene structure 1, thereby forming glassy carbon moieties within the original displacement to impart more desirable mechanical and electrical properties of the enhanced displacement.

In step 460, the method determines if the mechanical and thermal properties of an (i)th displacement have been sufficiently enhanced. If the method determines in step 460 that the mechanical and/or electrical properties of the treated displacement of step 440 does not comprise a desired compactability level and/or compressive strength, then the method transitions from step 460 to step 440, and continues as described herein.

Alternatively, if the method determines in step 460 that the mechanical and thermal properties of an (i)th displacement have been sufficiently enhanced, then the method transitions from step 460 to step 470 wherein the method determines if (i) equals (N), i.e. if each of the (N) displacements of step 410 have been treated. If the method determines in step 470 that (i) equals (N), then the method transitions from step 470 to step 490 and ends. Alternatively, if the method determines in step 470 that (i) does not equal (N), then the method transitions from step 470 to step 480 wherein the method sets (i) equal to (i+1). The method transitions from step 480 to step 440 and continues as described herein.

While the preferred embodiments of the present invention have been illustrated in detail, it should be apparent that modifications and adaptations to those embodiments may occur to one skilled in the art without departing from the scope of the present invention. 

We claim:
 1. A method to form a displacement, comprising: disposing a powder blend comprising a plurality of ground ceramic particles and a plurality of ground resin particles into a mold; densifying said powder blend while in said mold; heating said mold to form a first displacement; impregnating said first displacement with a polymer precursor compound to form a second displacement; and heating said second displacement to form a third displacement.
 2. The method of claim 1, wherein said impregnating step comprises: immersing said first displacement in a liquid mixture comprising said polymer precursor compound; monitoring a weight increase for said first displacement; when a weight of said first displacement no longer increases with time, determining that said second displacement is formed.
 3. The method of claim 1, wherein said heating said second displacement to form said third displacement step comprises heating said second displacement at about 1000° C. for about 24 hours.
 4. The method of claim 1, further comprising heating said first displacement at about 1000° C. for about 24 hours before impregnating said first displacement with said polymer precursor compound to form said second displacement.
 5. The method of claim 1, wherein said plurality of ground ceramic particles comprises a maximum dimension less than about 150 microns.
 6. The method of claim 1, wherein said plurality of ground resin particles comprises a maximum dimension less than about 100 microns.
 7. The method of claim 1, wherein said polymer precursor compound is selected from the group consisting of furfuryl alcohol, phenol formaldehyde oligomer, acetone-furfural, furfuryl alcohol-phenol oligomer, polyvinyl chloride oligomer, polyvinylidene chloride oligomer, polyacrylonitrile oligomer, and cellulose.
 8. The method of claim 7, wherein said polymer precursor compound is furfuryl alcohol.
 9. The method of claim 1, wherein said third displacement comprises glassy carbon moieties having ceramic particles disposed therein.
 10. The method of claim 9, wherein said glassy carbon moieties comprise a first polymer having a structure:


11. The method of claim 9, wherein said glassy carbon moieties comprise a second polymer having a structure:


12. The method of claim 9, wherein said glassy carbon moieties comprise a fullerene having a structure:


13. The method of claim 1, wherein said powder blend comprises a plurality of ground ceramic particles, a plurality of ground resin particles, and a plurality of reinforcing fibers.
 14. The method of claim 13, wherein said plurality of reinforcing fibers each comprises a length of about 200 microns.
 15. The method of claim 14, wherein said plurality of reinforcing fibers are formed from uncoated milled fiber glass.
 16. The method of claim 1, wherein said powder blend comprises a plurality of ground ceramic particles, a plurality of ground resin particles, and a cylindrical graphite member.
 17. The method of claim 16, wherein said cylindrical graphite member is partially encapsulated by said powder blend when disposing into said mold. 